To earn a patent the idea is supposed to be new and unique. Patents are not to be issued if the idea would be obvious to those skilled in the art.
Because of the 1963 un-patented Arctic Cat Ski, in my opinion, anyone can make a concave ski with dual runners. Because, it established the longitudinal triangular design on the bottom of a snowmobile ski.
The 1974, Richard Labelle patent abstract summed it up well. “A ski for snowmobiles in which the underface of the ski is provided with a central longitudinal groove with ground-engaging wear rods on each side of the groove, resulting in improved steerability for any snowmobile.”
Those skilled in the art know the “Laws of Physics” only work one way. Any ski that has a longitudinal triangular groove and is the same width, between the wear rods, will function similarly as long as they are attached the same way and have equal ski pressure. Their distinctions made them look different but functionally they would be similar. As the “Laws of Physics” dictate similar profiles follow similar ruts. (The path of least resistance.) Not only does the Simmons ski dart following other Simmons skis they also dart when following Ski Doo’s Precision skis. Darting occurs when the skis are grabbed in an unsafe manner by the ruts left by other similar profiled snowmobile skis.
For anyone skilled in the art it is obvious the only adjustments relate to ski pressure. The Twin Track makers found out to late. They had done all their testing on older sleds with little ski pressure. However, the sled OEM’s had recently shifted more weight onto the skis. The people at the 1980 Twin Track allowed customers to exchange their original ski for the revamped ski.
There were 4 options open to them to reduce the effort to turn the handlebars. They could shorten the ski, the outside edges or the runners. They could also reduce the height of the outside edges or a combination of all 4 options. In other words, reducing the profile “enough” is all that is required. The key is to maintain the improved floatation.
Flat vs V-Shaped ski
The concave design does improve floatation in deep snow by trapping the snow between the outside edges as it passes through. Turning on snow. However, most snowmobiling takes place on groomed packed trails with frequently icy corners.
For riding groomed trails the only benefit was temporary because 2 ½ years after Ski Doo came out with their Precision ski they both would slip into the grooves of the other. (Darting)
This design, functionally reduces the sleds ability to turn at speed on groomed trails because the weight is focused aprox. 2 ½” closer to the center of the sled.
As one skilled in the art, I would say a combination of the 4 options was obvious due to the increased ski pressure. Everything Simmons did was also obvious when making a functional plastic version of a longitudinal triangular steel ski!!! Plastic skis need more mass and more gradual contours to maintain rigidity, durability and some flexibility.
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